The overall goal of this research program is to understand the mechanisms that control assembly and maintenance of parallel sensory pathways in the mammalian brain. This proposal focuses on the question of whether axonal competition is important for the establishment and maintenance of RGC axon-target matching. Substantial progress has been made to identify roles for competitive interactions in the development of other key aspects of visual circuitry, such as eye-specific connections and retinotopic maps. The role of axonal competition in overall target selection, however, remains unresolved. To address this issue, several state-of- the-art tools for visualizing and manipulating specific sets of RGCs and their connections, including Cre- dependent ablation of RGCs, will be utilized. The specific aims of this proposal are to: 1) test the hypothesis that competition plays crucial role in the development of axon-target matching during embryonic development, 2) test the hypothesis that competition plays a crucial role in ensuring the maintenance of RGC axon-target specificity after their connections form, and 3) test the hypothesis that axonal competition is a key determinant on dendritic targeting. Results from these experiments should lead to new understanding of how neural circuits form and maintain wiring specificity in the mammalian brain. Additionally, information gained from these studies should contribute important insight into the possible origins of human developmental disorders stemming from errors in brain wiring.